Dino ignition problem

Whew! after an extensive overhaul some 700 miles later it developed a miss at low end but cleared up under full throttle. I did the whole syncro the carbs, air fuel mixture, Idle jet thing via Superformance instructions and Corbani experiance to no avail.
Finally I decided to do a compression check, (my worst fears were that I would have to break into the engine) Done that enough for sure. Well every thing checked out great with every cylinder within 5 psi of each other, so it has to be ingnition, wires, points or centrifigal advance. I have a MSD 6AL with an 8,000 rpm chip and some have said that the 8 chip can cause problems which are cleared up after changing. I am looking for possibilities and help.
Here's something, the rear bank plugs are buning clean and bright but the front bank plugs where the missing is coming from are black sooty which should indicate rich mixture on that side but the carbs have been adjusted tits at least three times. The carbs are newish and in very good shape and cleaned at overhaul. All jets (adjustable) were removed and air blown through the passages most recently.
I know some threads discussed having the air fuel jets( upper) screwed in all the way on one side. This was the case with its former adjustment but I followed the Superformance guidelines and I did adjust out the required 1-1/12 turns with no change in the missing pattern. I am pulling out my hair! Everything was running great and then ****. Suggestions much appreciated. Tnx

 

What plugs are you running?

On the overhaul did you change to high comp pistons.

Have you checked the leads? disy cap?

Black sooty plugs are a good indication you are rich, when you tighten up the thottle linkages do you check the airflow. Any increase when you re-tighten the linkages can have the front carbs drawing to much air.

Are the idle jets clean?

 

Tony thanks,
NGK BP7ES, Yes on the high compression pistons 10:1, no on checking the leads but deserves a check, they were new at the overhaul Accel 300+ Ferro Spiral Race Wire and I have checked the cap and it looks good with the internals looking good and no apparent cracks.

I have set and resynced (Uni-Syn) thee times and checked again after a warm-up drive and all check and flow indentical. On the idle jets I pulled all out and blew out the jets with air and reinstalled to specs suggested by superformance. Now its got to be something in the ingnition.

 

Slightly confused as to why the front bank gets the problem with sooty plugs and the rear bank is clean!!

It seems that the problem is common to the front bank and the thing that can be wrong is the carb set up. Odd that all three cyl's are affected, if it is ignition problem then it must be something that is common to the front bank. But why does it do it a low revs? Try swapping the rear plugs with the front ones and see what happens.

If the front set foul up and the rears are cleaned then it narrows down the search.

Could be the MSd controller, not familar with that one i am afraid. Is the coil OK.

Just purchased a new prog ignition system and kept getting misfiring at low revs, when i floored it, she shot up the road like a scalded cat. Cruised at 40mph, misfired.

Checked the coil and found she was running too hot (i mean really hot). Changed the coil as i thought it may be breaking down under load. Cured it

Is this MSD programmable?

The reason i asked about the plugs is that i used BP8 and got fouled plugs after an unleaded conversion, swapped to BP7 and they were OK.

 

Can't you rule out the coil since there is only one and common to all cylinders?

Just a wild thought, but doesn't the crankcase venting/EGR valve empty into the front bank somewhere?

 

Get an Expert to adjust the carbs !
Sometimes driving them with new sparkplugs helps.

 

Should be able to rule out ignition with your setup. I prefer to set carbs with air bypass screws as much in as possible but that should be a small problem. There might be a clue in the idea of oil vapor blowing back into the near carbs but with a new engine, that does not seem reasonable. Easy to test though, just remove the airbox cover and run for 20-30 miles and see what the plugs look like then. Let us know what you find. Thanks, John

 

Choke cable runs through each 3-cylinder bank as a unit. Could the choke cable be bound on the one side? If you have the choke cable connected, make sure that all of the choke levers are free to return to their stop!!!!

This will lead to exactly your symptom...!

Jim S.

 

Thanks John I really respect your input, during this episode I have kept the entire airbox cover removed and the engine bonnet also to allow complete access to all componants.
Now this is interesting about the air bypass jets as I have seen threads that say to bottom these out one front bank. Now is this a function of making an adjustment to compensate for a deficicency in the original layout of the Webers? The superformance guidelines direct you to adjust all the air bypass screws (six) to the same measurement without bottoming any of them. Right now I am very confused but my gut says that something in between my well be where I need to be, which I think is what you are suggesting.

 

Jim good call, I checked that and will readjust to be sure I am at full return.

 

Gary - Are the fouled plugs causing the misfire ? How have you arrived at that, or is it something else in the ignition + carbs. The fouled plugs could be a red herring.

I would suggest you turn out the air bypass screws 1.5 turns. Have you had a problem before with them at that setting, doubt it. It gives all the carbs a starting point for finer adjustment.

 

Tony, The air bypass are at 1.5 turns now, they were screwed in all the way at first on the front bank.

 

Looking at things in logical order, what affects the front and rear barrels. Each carb feeds cylinders 1-4,2-5,3-6. As the problems is the front bank, the common denominator is a few things.

Gary

Incorrectly adjusted bypass screws will normally cause a lean condition, snapping or popping thru the carbs. This is because too much air is diluting the mixture control setting. Setting to 1.5 turns of bottom is a starting point, the unisym is then used to balance out the airflow. Be careful though as too high idle speed setting lifts the butterflies above the progession ports, which will allow fuel to be drawn in thus causing and overich mixture. Also this can lift the accelrator pump circuit and cause droplets to splash onto the butterflies too. Having said that you would expect the problem to show on the opposite bank of cylinders. ie badly adjusted idle would affect
1-4,2-5 or 3-6.

So the problem could be a vaccum leak on the inlet manifold O rings, gaskets, you would get a popping back thru the carb/s, misfiring during acceleration, engine hunting at high speed, snapping back through the exhaust at deceleration. Yet again it has been known to have a badly fitting manifold?? Does the mixture screw adjustment to these banks have a noticibable effect? If they are slow to respond then it points to vac leak, plug spark u/s or plugged idle jets.

Yet again the symptoms you describe relate to something common to the front bank, what?

Can you tell me what happens if you fit fresh plugs and take it out for a good blast down the road. Does it misfire straight away ? What colour are the plugs on all cylinders. choclate brown is ideal.

Are you sure the misfire relates to the fouled plugs? With all three plugs fouled up, how does it start!!!!

Tony

 

Tony, much to think about and much to check, darn thing was running so good and then crap, so I will start with the basics and enlist some help to sort it out and report back if I make a discovery. Give me a little time to sort out and I thank you for your time spent. I will be getting back.

 

It only costs 200 euros for an expert to set up and check carbs here in Italy,their is alot of people that use tools and stuff to set up.But my carb Ferrari was set up by a Professional and since the 2 years he set it up by ear(no instruments) the car beats the hell out of 348s,its perfect.

Its easy for an inbalance and I seen modern mechanics which don't know nothing about carb adjustment.An expert with new Ferraris could not adjust my carbs,then I took it to the professional.
The professional balances the countach carbs by ear,and thats brilliance!

Why go insane and just get a carb guy to adjust them and your on the go!

Or does it cost thousands to do this job in the U.S?

 

Orlando, thank you for the words of wisdom. I am going to fully sort out the ingnition componants before doing just what you suggest. Its also been on my mind to convert the little jewel to fuel injection with a single large throttle body and save all the old parts. eliminate all the bugaboo's of the webers and get more drivability too.
I never plan sell it and my daughter in law wants to someday have it, so reliability is paramount.

 

Carbs go better than injection cars look at the 308 carb and the 308 i.Also carb BB and BBi.


Once I had problems with the sparkplug extensions which were dissipating electricity and not making the sparkplug have the correct spark ,it made a problem similar to yours.
I changed sparkplug extenders and sparkplugs and the car was going good again.

 

Gary

Just a thought, do you have the US disy with 6 lobe (single points) or the Euro 3 lobe ( 2points).

If you have the 3 lobe with dual points, is one set out of phase or moved?

I THINK i am correct in stating the one set does, 1,2,3 cylinders and the second set does 4,5,6 (hence the 1,4,2,5,3,6 firing order)

Worth a look if you haven't already tried it!!

It would certainly explain one bank misfiring

Cheers

Tony

 

Thanks Tony, I do have the dual points distributor and if I recall MSD mentions disconnecting one set of points so I tried the back set and it made no difference so now I will try the front set and see. I need to also check all plug wires with an ohm meter, it seems that one was very difficult to remove from the plug and required pliers. I will consider using some dielectic grease in the future.

 

I decided to change out the Accel wires for some MSD wires, looking for a better balance with the 6AL MSD unit and maybe eliminating a possible bad wire. The same problem existed after the change and so we started pulling plug wires while the engine was running. Cylinder no. 1 showed no change in RPM upon pulling the plug wire so we suspected a dead spark plug and changed that with no change to the low end miss. We then rechecked the compression with a 115-120 psi so now its to the distributor, cap or rotor. While I am in there I will completely go through and service the centrifical advance. All for now.

 

Centrifugal advance was junk, barely functioning and with bastard springs. I want to take to a fine tuned spec., where does one access the proper springs?

 

As far as i am aware they are not available anymore. Contact Ron at Superformance UK he may be able to help you.?

Tony

 

Bought the kit from Superformance.co.uk about 2 years ago. Fit and finish were bad and pins were not hardened. Cleaned up weights and used old hardened pins. Springs were fine and weights had right ballance. Adjusted diameter of phenolic inner stop tube on rotor shaft and played with washers behind springs. Was able to match published advance curve. Lubed everything and put back together. Been flawless for 2 years and 9,000+ miles. Have checked advance on car a couple of times. Always smooth to the right rpms. I just checked the Superformance site and the kit is now machine cut with hardened pins. Should be a good source.
John

 

Thanks John, all pins and weights are in perfect condition, including the drum with no indents, they were just gunked-up with hard dried grease and different weight springs with one very strong and bent. Looks like someone did a shade tree job on it. Thanks for the Superformance tip, I will check.

 

Completely serviced and replaced all springs and now finally have a functioning mech. advance. The carbs and exaust were still popping until I adjusted the air mixture screws in on the front side of the carbs. At this point I am adjusting by ear and I am much more satisfied with the results. Having a functioning advance really eliminates that flat or lag spot in the acceleration. I still don't know why we have to almost close off the front air mixture screws and I guess it doesn't matter as long as it works. This was written about in one of the threads but I have not encountered it as of late.